At least two people have been killed and scores wounded as Saudi police clashed with protesting foreign workers in a district of the capital, Riyadh.
A police statement said hundreds of people were arrested in the Manfuhah neighbourhood.
Later on Sunday, thousands of mostly African workers gathered in the capital to prepare for repatriation.
Last week police rounded up thousands of migrant workers after an amnesty linked to new employment rules expired.
One of the two people killed was a Saudi while the other was unidentified, police said. About 70 others were injured and there were some 560 arrests, officials added.
However, Ethiopian Foreign Affairs Minister Tedros Adhanom said he had information that three Ethiopian citizens had been killed, one last Tuesday and two in the latest clashes.
He said Addis Ababa had formally complained to Riyadh.
"This is unacceptable. We call on the Saudi government to investigate this issue seriously. We are also happy to take our citizens, who should be treated with dignity while they are there," he said.
Police said they intervened on Saturday after foreign workers in the Manfuhah district rioted, attacking Saudi and other foreign residents with rocks and knives.
Vigilante Saudi residents in Manfuhah reportedly joined the fighting and even detained some Ethiopians.
Manfuhah is home to many migrants, mostly from east Africa.
On Sunday, witnesses said police surrounded the district while units from the National Guard and special forces were sent in.
Hundreds of African migrants reportedly surrendered to police.
A long line of buses took the migrants to temporary housing along the airport road in Riyadh.
Last Monday, the authorities began rounding up thousands of illegal foreign workers following the expiry of a seven-month amnesty for them to formalise their status.
Nearly a million Bangladeshis, Indians, Filipinos, Nepalis, Pakistanis and Yemenis are estimated to have left the country in the past three months.
More than 30,000 Yemenis have reportedly crossed to their home country in the past 10 days alone.
Four million other migrants obtained work permits before last Sunday's deadline.
Saudi Arabia has the Arab world's largest economy, but authorities are trying to reduce the 12% unemployment rate among native Saudis.
An estimated nine million migrant workers are in Saudi Arabia - more than half the workforce - filling manual, clerical, and service jobs.